The derivation of human embryonic stem (ES) cell lines has opened up exciting new prospects for basic biomedical research and therapeutics in the new field of regenerative medicine. In order for human ES cells to fulfill their potential, it will be necessary to understand a good deal more about the control of their growth and differentiation. The broad goal of this project is to identify the extrinsic factors that control the growth and differentiation of human ES cells and committed progenitor cells, in order to improve in our ability to grow ES cells and produce specific types of specialized cells from them in significant quantities. Focusing on the role of cell interactions in vitro, particularly between the pluripotent stem cells and cells resembling extraembryonic endoderm, a tissue now recognized to play a key regulatory role in determining cell fate in the early mammalian embryo, the first aim is to identify growth and differentiation factors, which modulate these cell interactions. The major focus here will be members of the transforming growth factor beta superfamily and their antagonists, which play important roles in early embryo development. The second aim of the project is to study the action of these candidate factors on ES cells and cells at early stages of commitment to various differentiation lineages. The third aim of this proposal is to identify isolate and characterize committed progenitor cell populations from ES cell cultures. These cell populations will be isolated either from spontaneously differentiating ES cetl cultures or from ES cultures undergoing directed differentiation, using specific culture conditions and immunoisolation methodology developed in preliminary studies or during the course of this project. The work undertaken in this project will result in the ability to obtain and amplify committed populations of progenitor cells from human ES cultures, in particular precursors of neural and endodermal lineages, and to use these progenitors to produce specific types of differentiated cells. The ability to generate committed stem cell populations from ES cells and in turn derive highly enriched populations of end cells from these precursors will greatly enhance the utility of human ES cells in basic research (the study of human gene function in health and disease and the development of new drugs) and in transplantation medicine. This project will use stem cell lines ES 01 02 03 04 05 06 on the NIH Embryonic Stem Cell Registry.